Chairs have back rests which are typically intended to provide support for the user's back in the area between the shoulders and the waist. In order to accommodate the varying physical sizes of individual users, many chairs have a back rest that is vertically adjustable or tiltable relative to the chair seat. Unfortunately, typical height adjusting or tilting mechanisms have suffered from undue complexity, difficulty in assembly, unsightly appearance and difficulty in operation. Many such mechanisms have also required the user to operate them with both hands or have required the user to use tools to adjust the mechanism. Another deficiency with many back rest mechanisms is that the user is required to leave the chair in order to adjust the height of the back rest and then reoccupy the chair to determine whether the proper height has been attained.
Many typical back rests, especially unitary molded back rests, have lacked the ability to withstand the applied forces and thus have been subject to structural failure caused by stress-induced cracks resulting from flexing. The cushions used in these back rests have also been difficult and expensive to manufacture because they must be pre-formed in particular shapes and sizes to conform to the curvature of the human back.